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  • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
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  • H10K30/80—Constructional details
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
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  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/80—Constructional details
  • H10K30/81—Electrodes
  • H10K30/82—Transparent electrodes, e.g. indium tin oxide [ITO] electrodes
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
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  • H10K39/32—Organic image sensors
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  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
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  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
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  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
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  • H10K85/151—Copolymers
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
  • H10K85/211—Fullerenes, e.g. C60
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
  • H10K85/211—Fullerenes, e.g. C60
  • H10K85/215—Fullerenes, e.g. C60 comprising substituents, e.g. PCBM
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
  • H10K2102/10—Transparent electrodes, e.g. using graphene
  • H10K2102/101—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO]
  • H10K2102/103—Transparent electrodes, e.g. using graphene comprising transparent conductive oxides [TCO] comprising indium oxides, e.g. ITO
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/549—Organic PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• This invention relates to an organic photodetector (OPD) having excellent optical sensitivity in a favorably narrow wavelength region and allows to tune the response to different wavelengths depending on the desired application.
• OPD organic photodetector
• methods of producing said organic photodetectors and methods of tuning the resonance of a microcavity formed in an organic photodetector (OPD) to a predetermined wavelength are disclosed.
• Organic photodetectors are usually configured so as to comprise n- and p-type organic semiconductors sandwiched between two electrodes, optionally in combination with auxiliary layers, such as e.g. hole and electron extraction layers.
• FWHM full width-half maximum
• EQE external quantum efficiency
• optical filters such as notch filters.
• the implementation of optical filters requires additional processing steps and often involves limitations with respect to the possible device geometries and device integration, so that finding alternatives is desirable.
• microcavity photodiodes which comprise a configuration, wherein a bilayer consisting of a spin-coated layer of the semiconducting polymer MeLPPP and a fullerene layer is provided on an indium tin oxide (ITO) covered dielectric mirror.
• ITO indium tin oxide
• the resonance of the microcavity may be tuned to specific wavelengths by varying the thickness of the MeLPPP polymer layer.
• the EQE performance of these devices still leaves room for improvement as adjusting the active layer thickness in order to shift the resonance wavelength to the desired region tend to negatively affect the device sensitivity and the transmission properties of the microcavity.
• This invention describes organic photodetectors wherein an optical cavity is used to tune the response to a specific wavelength range of interest while suppressing the sensitivity outside the said wavelength range, in combination with an active layer made of materials with relatively low absorption at the cavity resonance wavelength in order to allow an exceptionally narrow spectral response and simultaneously high external quantum efficiency without requiring the use of optical filters.
• an organic photodetector comprising: a microcavity defined by a reflective electrode and a semi-transparent electrode, wherein the microcavity comprises a transparent conductive oxide layer and an active layer comprising an n-type organic semiconductor and a p-type organic semiconductor; and wherein the transmittance T of the active layer at the wavelength K max is at least 50%,
• a ma x being the wavelength of the maximum of the external quantum efficiency (EQE) spectrum of the organic photodetector (OPD) at a desired range measured according to ASTM E1021 .
• the version of ASTM E1021 is E1021 -15 published in 2015.
• the present invention relates to a method of manufacturing an organic photodetector (OPD) comprising: providing a transparent conductive oxide layer and an active layer between a first semi-transparent electrode which is reflective and a second semi-transparent electrode which define a microcavity, wherein the active layer comprises a blend of an n-type organic semiconductor and a p-type organic semiconductor; and wherein the n-type organic semiconductor and the p-type organic semiconductor are selected so that the absorption spectrum of the blend meets the above definition.
• OPD organic photodetector
• Another aspect of the present invention is a method of tuning the resonance of a microcavity formed in an organic photodetector (OPD) to a predetermined wavelength, the organic photodetector (OPD) comprising a microcavity between a first semi-transparent electrode and a second semi-transparent electrode which is reflective, and the microcavity comprising a transparent conductive oxide layer and an active layer comprising a blend of an n-type organic semiconductor and a p-type organic semiconductor; the method comprising a step of adjusting the thickness of the transparent conductive oxide layer in order to shift the resonance wavelength of the microcavity to the predetermined wavelength.
• OPD organic photodetector
• FIG. 1 schematically illustrates an exemplary configuration of an organic photodetector (OPD) according to the present invention.
• FIG. 2 shows the external quantum efficiency (EQE) spectra at different conductive oxide layer and active layer thicknesses.
• the present invention relates to an organic photodetector (OPD) comprising: a microcavity defined by a reflective electrode and a semi-transparent electrode, wherein the microcavity comprises a transparent conductive oxide layer and an active layer comprising a blend of an n-type organic semiconductor and a p-type organic semiconductor; and wherein the transmittance T of the active layer at a wavelength A ma x is at least 50%, A ma x being the wavelength of the maximum of the external quantum efficiency (EQE) spectrum of the organic photodetector (OPD) at a desired range measured according to AST E1021 (Standard Test Method for Spectral Responsivity Measurements).
• OPD organic photodetector
• EQE external quantum efficiency
• microcavity denotes an optical resonator, typically having a wavelength scale, the structure of which exhibits spectral selectivity due to resonant optical modes in the cavity between the reflective electrode and the semi- transparent electrode.
• the dimensions of the optical zone defining the microcavity along the direction of light propagation are on the order of at no more than a few (approximately four) wavelengths of the incident radiation.
• the active layer comprising the blend of the n-type organic semiconductor and the p-type organic semiconductor exhibits a transmittance T at the wavelength K max of at least 50%, preferably at least 60%, more preferably at least 70%, for example at least 80%, it is ensured that the active layer absorption at the main resonance wavelength of the microcavity is low, since the relationship between transmittance T and absorbance will be basically defined by the following equation according to the Beer-Lambert law, wherein k is the extinction coefficient (absorptivity coefficient) of the active layer, d is the thickness of the active layer, and Ama is the wavelength of the maximum of the external quantum efficiency (EQE) spectrum:
• the method of determination of the transmittance is not particularly limited and may involve spectrophotometric methods known in the art.
• the organic photodetector of the present invention exhibits a (preferably global) EQE maximum within a wavelength range of between 400 to 700 nm, such as 460 to 600 nm, more preferably between 500 and 560 nm (cyan/green).
• the organic photodetector may exhibit a FWHM in the EQE spectrum of less than 80 nm, more preferably less than 50 nm, which is a remarkable improvement over comparable prior art devices.
• the n-type organic semiconductor and a p-type organic semiconductor are comprised in the form of a blended layer, which remarkably simplifies the processing method when compared to the manufacture of a bi-layer structure comprising neat films of each the n-type organic semiconductor and the p-type organic semiconductor.
• the n-type organic semiconductor is not particularly limited and may be suitably selected from electron accepting materials known to the skilled artisan in dependence of its absorption at the resonance wavelength in order for the blend to meet the above-defined criteria.
• fullerenes and fullerene derivatives may be mentioned.
• the n-type organic semiconductor is selected from Ceo, C70, C96, PCBM-type fullerene derivatives (including phenyl-C61 -butyric acid methyl ester (C60PCBM), TCBM-type fullerene derivatives (e.g.
• the n-type organic semiconductor is preferably C60 fullerene derivative. It is understood that the n-type organic semiconductor may also consist of a mixture of a plurality of the above electron accepting materials.
• the p-type organic semiconductor is likewise not particularly limited and may be appropriately selected from standard electron donating materials that are known to the person skilled in the art and are described in the literature.
• the p-type organic semiconductor is an organic conjugated polymer, which can be a homopolymer or copolymer including alternating, random or block copolymers. Preferred are non-crystalline or semi-crystalline conjugated organic polymers.
• polymers selected from conjugated hydrocarbon or heterocyclic polymers including polyacene, polyaniline, polyazulene, polybenzofuran, polyfluorene, polyfuran, polyindenofluorene, polyindole, polyphenylene, polypyrazoline, polypyrene, polypyridazine, polypyridine, polytriarylamine, poly(phenylene vinylene), poly(3-substituted thiophene), poly(3,4-bisubstituted thiophene) , polyselenophene, poly(3- substituted selenophene), poly(3,4-bisubstituted selenophene), poly(bisthiophene) , poly(terthiophene), poly(bisselenophene) , poly(terselenophene), polythieno[2,3- b]thiophene, polythieno[3,2-b
• Preferred examples of p-type OSCs are copolymers of polyfluorenes and polythiophenes, each of which may be substituted, and polymers comprising benzothiadiazole-based and thiophene-based repeating units, each of which may be substituted.
• the p-type organic semiconductor may also consist of a mixture of a plurality of electron donating materials.
• the p-type organic semiconductor is a polymer having a structural unit represented by the following formula (1 ):
• Ar 1 and Ar 2 are the same as or different from each other and represent a trivalent heterocyclic group;
• R 3 , R 4 , R 5 , R 6 , R 7 , and R ⁇ 8 are the same as or different from each other and represent a hydrogen atom, a halogen atom, an alkyl group, an alkyloxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an arylalkyl group, an arylalkyloxy group, an arylalkyl
• the p-type organic semiconductor is a conjugated organic polymer formed from monomers comprising one or more units according to structural formulae (2) and/or (3):
• R 9 and R 12 are independently selected from hydrogen, a halogen, C1-C20 hydrocarbyl, particularly C1 -C20 alkyl, C1-C20 hydrocarbyl containing one or more S, N, O, P or Si atoms;
• R 3 and R 4 are independently selected from hydrogen, C1 -C30 hydrocarbyl, particularly C1 -C30 alkyl, C1-C30 hydrocarbyl containing one or more S, N, O, P or Si atoms;
• R 13 and R 14 are independently selected from hydrogen, a halogen, particularly fluorine,
• R 9 and R 12 represent hydrogen
• R 10 and R 11 are independently selected from a C1 -C30 alkyl group
• R 13 and R 14 represent fluorine.
• the thickness of the active layer may be suitably adjusted by the skilled artisan and is typically in the range of from 50 to 500 nm, preferably from 100 to 350 nm.
• the transparent conductive oxide layer may be made of materials including e.g. indium tin oxide (ITO), gallium tin oxide, zinc indium tin oxide, indium tin oxide (ITO) being preferred.
• the sum of thicknesses of the active layer and the transparent conductive oxide layer is typically in the range of from 60 to 450 nm.
• specific organic photodetector devices are known, which allow tuning of the spectral photoresponse by varying the thickness of the active layer (see e.g. R. Koeppe et al., Applied Physics Letters 2003, 82(16), 2601 -2603; J. M. Lupton et al, Advanced Materials 2003, 15(17), 1471 -1474).
• the resonance wavelength may be tailored by varying the thickness of the transparent conductive oxide layer.
• the present invention enables optimizing the thickness of the active layer in terms of optical properties and a favourable EQE photoresponse, and subsequently fine-tuning the conductive oxide layer thickness in order to shift the device sensitivity to the desired wavelength.
• typical transparent conductive oxide layer thicknesses may be in the range of from 10 to 150 nm, in embodiments in the range of from 20 to 100 nm.
• the semi-transparent electrode is an anode, more preferably a top anode, wherein "top” denotes a position remote from a substrate structure (if present) and close to the surface at which incoming radiation enters the detector.
• the semi-transparent electrode may be made of a layer of metal(s) (such as Au, Ag, Al, In etc.), for example, with Ag being preferred, wherein the layer thickness is typically in the range of from 5 to 100 nm, and wherein the optical transmittance is usually between 80% and 1 %.
• the reflective electrode is configured to reflect at least a portion of light and to induce optical resonance together with the semi-transparent electrode, and may also transmit a portion of light to be itself semi-transparent.
• suitable material for the preparation of the reflective electrode thin layers of metals or metal alloys may be mentioned.
• the reflective electrode is formed of silver (Ag), silver alloys (including Ag— Cu— Au (ACA) or Ag— Pd— Cu (APC)), or aluminum (Al). It is to be understood that the reflective electrode may be configured so as to comprise a plurality of layers as long as one surface thereof is reflective so as to form the optical cavity.
• HTL hole-transporting layers
• EBL electron blocking layers
• ETL electron transporting layers
• spacer layers connecting layers and hole-blocking layers (HBL)
• a hole transport layer (HTL) or an electron blocking layer (EBL) may include poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOTPSS), polyarylamine, poly(N-vinylcarbazole) , polyaniline, polypyrrole, N,N, N',N'-tetrakis(4- methoxyphenyl)-benzidine (TPD), 4-bis[N-(1 -naphthyl)-N-phenyl-amino]phenyl (a-NPD), m-MTDATA, 4,4',4"-tris(N-carbazolyl)-triphenylamine (TCTA), and a combination thereof, without being limited thereto.
• PEDOTPSS poly(styrenesulfonate)
• PDOTPSS poly(styrenesulfonate)
• PDOTPSS polyarylamine
• the electron blocking layer (EBL) may further be an electron blocking layer in accordance with WO 2007/017475 A1 , for example, in order to reduce dark current.
• An electron transport layer (ETL) or a hole blocking layer (HBL) may include one selected from, for example, 1 ,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA), bathocuproine (BCP), LiF, Alq3, Gaq3, lnq 3 , Znq 2 , Zn(BTZ) 2 , BeBq 2 , and a combination thereof, for example.
• the organic photodetector according to the present invention may include an optical spacer layer.
• the materials and thicknesses of such layers may be suitably selected by the skilled artisan.
• suitable materials include, but are not limited to, TiOx, bathocuproine (BCP), C 6 o, or molybdenum oxide (Mo0 3 ), molybdenum oxide being preferred.
• the organic photodetector according to the present invention may further comprise a substrate layer may be produced from a glass, from a flexible plastic or metal film or any other conventional material, and while not being limited thereto, its thickness is typically in a range of 100 nm to 5 mm.
• the organic photodetector (OPD) according to the present invention may comprise a protective layer which may be made of conventional inorganic or organic materials known in the art used to prevent physical and/or chemical damage (by moisture or oxygen, for example).
• the organic photodetector has a configuration, wherein the transparent conductive layer is provided over the reflective electrode (at the entire surface or a part thereof), the active layer is provided over the transparent conductive layer (optionally in contact with the reflective electrode) , and the semi-transparent electrode is provided over the active layer (preferably with a hole transport layer in between).
• FIG. 1 An exemplary configuration of an organic photodetector according to the present invention is shown in Fig. 1 .
• a reflective cathode 2 is provided in contact with a substrate layer 1.
• a bilayer stack consisting of a transparent conductive layer 3 and an hole blocking layer 4 is deposited on the reflective cathode 2, with the transparent conductive layer 3 being in contact with the latter.
• the active layer 5 comprising a blend of the n-type and p-type organic semiconductor is deposited onto the bilayer stack.
• a hole transport layer 6 is provided between and in contact with the active layer 5 and a semi-transparent anode 7.
• a protective layer 8 is provided on top of the semi-transparent anode 7. While such a configuration has been shown to exhibit particularly favourable photoresponse characteristics, it is understood that the present invention is not limited to said configuration.
• the presence of the hole transport layer, the substrate layer and the hole blocking layer is merely optional.
• OPD organic photodetector
• the organic photodetector (OPD) described above exhibits a favourable photoresponse which enables effective and efficient color discrimination since particularly narrow FWHM and high EQE values may be simultaneously attained, so that wavelength sensitivity may be dramatically improved without the use of optical filters. Accordingly, in a preferred embodiment, the OPD according to the present invention does not comprise an optical filter, such as e.g. a notch filter.
• the resonance wavelength of the microcavity may not only be altered by varying the active layer thickness but also by the variation of the total thickness of the transparent conductive oxide layer and the active layer comprising the blend of an n-type organic semiconductor and a p-type organic semiconductor.
• the active layer thickness it is possible to set the active layer thickness to an optimized value in terms of EQE efficiency, processability etc. , and to then tune the microcavity resonance wavelength by adjusting the conductive oxide layer thickness without substantially affecting the OPD performance.
• the present invention may also be advantageous in cases where low amounts of the active layer material are available or where processing of particularly thin or thick active layer films is difficult.
• the present invention relates to a method of tuning the resonance of a microcavity formed in an organic photodetector (OPD) to a predetermined wavelength, the organic photodetector (OPD) comprising a microcavity between a first semi-transparent electrode and a second semi-transparent electrode which is reflective, and the microcavity comprising a transparent conductive oxide layer and an active layer comprising a blend of an n-type organic semiconductor and a p-type organic semiconductor; wherein the method comprises a step of adjusting the thickness of the transparent conductive oxide layer in order to shift the resonance wavelength of the microcavity to the predetermined wavelength.
• OPD organic photodetector
• said method preferably further comprises a step of adjusting the transmittance T of the active layer at the wavelength h max to a value of at least 50%, preferably at least 60%, more preferably at least 70%, for example at least 80%, which may be accomplished by selecting a material blend having an appropriate extinction coefficient and/or by varying the active layer thickness, for example.
• the photodetector used in this method and its constituents may exhibit the properties set out in the above description of the organic photodetector (OPD).
• the present invention relates to a method of manufacturing of an organic photodetector (OPD) according to the above description, the method comprising: providing a transparent conductive oxide layer and an active layer between a first semi-transparent electrode which is reflective and a second semi-transparent electrode which define a microcavity, wherein the active layer comprises a blend of an n-type organic semiconductor and a p-type organic semiconductor; and wherein the n-type organic semiconductor and the p-type organic semiconductor are selected so that the active layer comprising the blend of the n-type organic semiconductor and the p-type organic semiconductor exhibits a transmittance T of at least 50%, at the wavelength being the wavelength of the maximum of the external quantum efficiency (EQE) spectrum of the organic photodetector (OPD) at a desired range measured according to ASTM E1021.
• EQE external quantum efficiency
• the method of designing of the organic photodetector may further comprise a step of adjusting the thickness of the transparent conductive oxide layer in order to tune the resonance wavelength of the microcavity to the desired value.
• the layers constituting the organic photodetector may be fabricated by deposition techniques according to conventional methods known in the art, including photolithographic methods, sputtering techniques, thermal deposition, vacuum deposition, laser deposition, screen printing, printing, imprinting, spin casting, dipping, ink-jetting, roll coating, flow coating, drop casting, spray coating, and/or roll printing, for example.
• Exemplary organic photodetectors having an inverted structure in accordance with the configuration of Fig.1 have been manufactured, using Ag as material for the semi- transparent top anode and the reflective electrode, and as the material for the active layer a blend of ⁇ as the n-type organic semiconductor and a p-type organic semiconductor according to structural formula (A)
• Both CeoPCBM and compound (A) are characterized by a low absorbance around the target wavelength 550 nm (green) and exhibit absorption maxima at about 430 nm (CeoPCBM and Compound (A)), 720 nm (Compound (A)) and 800 nm (Compound (A)). It is ensured that the transmittance T of the active layer comprising the blend of CeoPCBM and compound (A) at 550 nm (A ma x) is at least 50% at the thicknesses given in the examples below.
• an ITO layer having a thickness of 45 nm was deposited onto the reflective Ag cathode, whereas the active layer thickness was 1 60 nm, which results in a total thickness of active and conductive oxide layers of 205 nm.
• An organic photodetector was prepared in accordance with Example 1 , with the exception that the ITO layer had a thickness of 25 and the active layer thickness was 1 80 nm.
• a further organic photodetector was prepared in accordance with Example 1 , with the exception that the ITO layer had a thickness of 80 nm and the active layer thickness was 140 nm, resulting in a total thickness of active and conductive oxide layers of 220 nm.
• the external quantum efficiency of each of the exemplary organic photodetectors was measured in a wavelength range of about 400 to 700 nm using a calibrated IPCE measurement system.
• the FWHM is calculated as width of a wavelength corresponding to a half of maximum EQE using a Gaussian fitting curve of the central EQE peak.
• EQE external quantum efficiency

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